Task states (Ready, Running, Blocked, Suspended) in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a task state to Ready.

FreeRTOS

eTaskState state = [1];

Drag options to blanks, or click blank then click option'

AeRunning

BeReady

CeBlocked

DeSuspended

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing Running instead of Ready, which means the task is currently executing.

The eReady state means the task is ready to run but not currently running.

2fill in blank

medium

Complete the code to check if a task is currently Running.

FreeRTOS

if (eTaskGetState(taskHandle) == [1]) {
    // Task is running
}

Drag options to blanks, or click blank then click option'

AeReady

BeBlocked

CeRunning

DeSuspended

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing Ready with Running state.

The eRunning state means the task is currently executing on the CPU.

3fill in blank

hard

Fix the error in the code to correctly set a task to Blocked state.

FreeRTOS

vTaskDelay([1]); // Delay causes task to enter Blocked state

Drag options to blanks, or click blank then click option'

A100

BportMAX_DELAY

C0

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero or negative values which do not block the task.

Using a positive delay value like 100 ticks causes the task to enter Blocked state for that time.

4fill in blank

hard

Fill both blanks to create a task and then suspend it.

FreeRTOS

xTaskCreate(taskFunction, "Task", 1000, NULL, 1, &taskHandle);
vTask[1](taskHandle); // Suspend the task
// Later
vTask[2](taskHandle); // Resume the task

Drag options to blanks, or click blank then click option'

ASuspend

BResume

CDelete

DStart

Attempts:

3 left

💡 Hint

Common Mistakes

Using Delete instead of Suspend, which removes the task permanently.

vTaskSuspend() pauses the task, and vTaskResume() restarts it.

5fill in blank

hard

Fill all three blanks to create a dictionary of task states for given tasks.

FreeRTOS

eTaskState states[] = {
    [1],
    [2],
    [3]
};

Drag options to blanks, or click blank then click option'

AeReady

BeRunning

CeBlocked

DeSuspended

Attempts:

3 left

💡 Hint

Common Mistakes

Repeating the same state multiple times.

This array holds three task states: Suspended, Running, and Blocked.

Practice

1.

Which FreeRTOS task state means the task is waiting to be assigned CPU time but is ready to run?

easy

A. Suspended

B. Running

C. Blocked

D. Ready

Solution

1. Step 1: Understand the meaning of Ready state

   The Ready state means the task is prepared and waiting for CPU time but is not currently running.

2. Step 2: Compare with other states

   Running means the task is currently executing. Blocked means waiting for an event. Suspended means paused by user.

3. Final Answer:

   Ready -> Option D

4. Quick Check:

   Ready = waiting to run [OK]

Hint: Ready means waiting but able to run soon [OK]

Common Mistakes:

• Confusing Ready with Running
• Thinking Blocked means ready
• Mixing Suspended with Blocked

2.

Which of the following is the correct way to suspend a task in FreeRTOS?

void suspendTask(TaskHandle_t task) {
    // What function to call?
}

easy

A. vTaskBlock(task);

B. vTaskSuspend(task);

C. vTaskReady(task);

D. vTaskRun(task);

Solution

1. Step 1: Recall FreeRTOS API for suspending tasks

   The function to suspend a task is vTaskSuspend(), which pauses the task until resumed.

2. Step 2: Verify other options

   vTaskBlock() and vTaskReady() do not exist as API calls. vTaskRun() is not a FreeRTOS function.

3. Final Answer:

   vTaskSuspend(task); -> Option B

4. Quick Check:

   Suspend task = vTaskSuspend() [OK]

Hint: Suspend tasks with vTaskSuspend() function [OK]

Common Mistakes:

• Using non-existent functions
• Confusing suspend with block
• Trying to run tasks manually

3.

Consider this FreeRTOS code snippet:

void vTaskFunction(void *pvParameters) {
    for (;;) {
        if (xSemaphoreTake(xSemaphore, 0) == pdTRUE) {
            // Critical section
        } else {
            vTaskDelay(pdMS_TO_TICKS(100));
        }
    }
}

What is the state of the task when vTaskDelay() is called?

medium

A. Running

B. Ready

C. Blocked

D. Suspended

Solution

1. Step 1: Understand vTaskDelay effect

   Calling vTaskDelay causes the task to enter Blocked state, waiting for the delay time to expire.

2. Step 2: Confirm task state during delay

   While delayed, the task is not Ready or Running; it is Blocked until the timer expires.

3. Final Answer:

   Blocked -> Option C

4. Quick Check:

   vTaskDelay = Blocked state [OK]

Hint: vTaskDelay puts task in Blocked state [OK]

Common Mistakes:

• Thinking delay means Ready
• Confusing Blocked with Suspended
• Assuming task runs during delay

4.

Identify the error in this FreeRTOS task management code:

vTaskSuspend(NULL);
vTaskResume(NULL);
vTaskResume(xTaskHandle);

What is wrong with this code?

medium

A. vTaskResume(NULL) is invalid and causes error

B. Cannot suspend current task with NULL parameter

C. vTaskResume requires task handle, NULL is allowed

D. No errors, code is correct

Solution

1. Step 1: Check vTaskSuspend(NULL) usage

   Passing NULL to vTaskSuspend suspends the current task, which is valid.

2. Step 2: Check vTaskResume(NULL) usage

   Passing NULL to vTaskResume is invalid and causes an error because NULL is not a valid task handle to resume.

3. Final Answer:

   vTaskResume(NULL) is invalid and causes error -> Option A

4. Quick Check:

   vTaskResume(NULL) causes error [OK]

Hint: vTaskResume(NULL) is invalid, must use valid handle [OK]

Common Mistakes:

• Assuming NULL resumes current task
• Confusing suspend and resume parameters
• Ignoring NULL parameter rules

5.

You want to create a task that waits for a button press event without using CPU time unnecessarily. Which task state should the task enter while waiting?

hard

A. Blocked

B. Ready

C. Running

D. Suspended

Solution

1. Step 1: Understand waiting without CPU use

   To avoid wasting CPU, the task should not be Running or Ready while waiting.

2. Step 2: Choose appropriate waiting state

   Blocked state is used when a task waits for an event like a button press, so it sleeps until event occurs.

3. Step 3: Differentiate from Suspended

   Suspended means paused by user, not event-driven waiting.

4. Final Answer:

   Blocked -> Option A

5. Quick Check:

   Wait for event = Blocked state [OK]

Hint: Wait for event = Blocked to save CPU [OK]

Common Mistakes:

• Using Suspended instead of Blocked
• Keeping task Ready and wasting CPU
• Confusing Running with waiting